The present invention pertains generally to infrared lasers and more particularly to stimulated Raman scattering utilizing rotational transitions in a diatomic molecular gas.
Various methods have been disclosed for shifting frequencies of conventional laser outputs in the IR spectrum. These methods have included four-wave mixing as disclosed in commonly assigned application Ser. No. 787,415 filed Apr. 14, 1977 by Richard F. Begley et al. entitled "Resonantly Enhanced Four-Wave Mixing," now U.S. Pat. No. 4,095,121 issued June 13, 1978 and Raman scattering as disclosed in commonly assigned application Ser. No. 466,583 filed May 2, 1974 by C. D. Cantrell et al. entitled "Infrared Laser System," now U.S. Pat. No. 4,061,921 issued Dec. 6, 1977 of which the present invention comprises an improvement.
In each of these systems and other previous systems for IR frequency shifting to a broad range of frequencies, simplicity and overall efficiency are important factors for economic utilization of the device. By minimizing the steps required for frequency shifting, such as the elimination of the Raman spin flip laser as set forth in the above disclosed application Ser. No. 466,583, the device can be simplified to reduce problems inherent in more complex systems.
Since the stimulated Raman effect can be produced in a single step with high conversion efficiencies, Raman shifting of a CO.sub.2 laser output provides high overall efficiencies because of the high efficiencies and well developed technology of CO.sub.2 lasers. However, Raman gain in gaseous media such as H.sub.2, D.sub.2, T.sub.2, HD, HT, or DT in the infrared requires threshold powers for stimulated Raman scattering which are near the breakdown threshold of the diatomic molecular gas for single pass focused geometry, such as suggested by Robert L. Byer, in an article entitled "A 16 .mu.m Source for Laser Isotope Enrichment" published in IEEE J. of Quantum Electronics, Vol. QE-12-732-733, November 1976.